Over the last several decades, propylene polymers have become of great importance in several end use applications. From packaging for consumer goods to automotive components, propylene polymers have demonstrated wide applicability. Useful propylene polymers may generally be produced using Ziegler-Natta catalysts comprising 1) a solid titanium catalyst component consisting of a titanium compound, a magnesium compound, and an internal electron donor, 2) a co-catalyst such as an organoaluminum compound, and 3) external electron donors. The art is full of attempts of variations and specific combinations of the aforementioned catalyst components. The art has recognized that such variations and combinations are both unpredictable but advantageously influential on copolymer properties. Therefore, the discovery of more variations and combinations of external electron donors, among other components, to accompany solid titanium catalyst has been of great benefit to improving the efficiency of the catalyst systems and the control of the polymer properties.
For example, external electron donors are used to control the stereoregularity and form of the polymer. Although a broad range of compounds are known generally as electron donors, a particular catalyst may have a specific compound or combinations of compounds with which it is especially compatible. Discovery of an appropriate type of electron donor can lead to significant improvements in the properties of the polymer such as molecular weight distribution and melt flow rate. Discovery of specific combinations of electron donors for solid titanium based supported catalysts that would provide beneficial results would be highly advantageous in certain applications.
The present invention fulfills this need by providing for propylene polymers and polymerization processes including a mixture of at least two electron donors, such as tetraethoxysilane (“TEOS”), methylcyclohexyldimethoxysilane (“MCMS”), propyltrimethoxysilane (“PTMS”), propyltriethoxysilane (“PTES”), methyltrimethoxysilane (“MTMS”), dimethyldimethoxysilane (“DMDMS”) and dicyclopentyldimethoxysilane (“DCPMS”) in combination with a solid titanium catalyst system. Such combinations advantageously provide for a better balance of propylene polymer properties as can be observed, for example, through broad molecular weight distributions, high xylene solubles and fast crystallization kinetics.